Polyacrylate, commonly referred to as Plexiglas.RTM. (Rohm & Haas), is a popular plastic used for a variety of construction applications including glazing and roofing. Primerless adhesion to polyacrylate is, therefore, a an important property for room temperature vulcanizable (RTV) elastomers and sealants in the marketplace. Translucent, room temperature curable, silicone sealants frequently demonstrate adequate auto-adhesion to glass, aluminum, and PVC plastic. Adhesion to other plastics, for example polyacrylate, is much more difficult to achieve. For example, translucent, alkoxy curing, RTV compositions disclosed by Lucas et al. U.S. Pat. Nos. 4,483,973 and 4,528,353, utilizing amino functional silane adhesion promoters show excellent long term primerless adhesion to glass, metals, ceramics/mortar, and a variety of plastics including ABS, Noryl.RTM., polystyrene, and nylon, but do not adhere to polyacrylate.
Wengrovius and Lucas, U.S. Pat. No. 5,175,057, herewith incorporated by reference, disclose a 1-component, alkoxy curing, dialkyltin-bis-diketonate catalyzed RTV's containing and adhesion promoter which is the reaction product of an "M,D,T" silanol fluid and alkoxy silane functionalized by radicals selected from amino, ether, epoxy, isocyanato, cyano, acryloxy and acyloxy. Wengrovius '057 does not teach auto-adhesion to polyacrylate. Lucas, U.S. Pat. No. 5,232,982, herewith incorporated by reference, discloses scavenger reduced, alkoxy, RTV compositions having improved primerless adhesion to plastics, particularly polycarbonate. However, Lucas '982 does not teach primerless adhesion to polyacrylate.
The use of titanium chelates as self bonding agents for alkoxy curing RTV's is disclosed by Lucas in U.S. Pat. No. 4,680,364. The RTV compositions of U.S. Pat. No. 4,680,364 are filled with fumed silica, have limited self bonding to polyacrylate and suffer the limitation of opacity due to the poor solubility of the titanium chelates in PDMS.
There are numerous other examples, in the Patent literature, describing self bonding, 1-part, RTV compositions for example; Ashby and Lucas, U.S. Pat. No. 4,506,058; Beers U.S. Pat. Nos. 4,100,129 and 4,514,529; Mitchell, U.S. Pat. No. 4,273,698; Leempol U.S. Pat. No. 4,962,152; Inoue et al., U.S. Pat. No. 4,623,693; Letofie, U.S. Pat. No. 4,672,003; Hirai et al., U.S. Pat. No. 4,891,393; and Progneaux and Trego, U.S. Pat. No. 4,585,821. None of these references, however, teach auto or self-adhesion of room temperature vulcanizable silicone elastomers to polyacrylate.
Thus, there continues to be a need to provide a curable RTV silicone composition containing a reinforcing inorganic filler, having the combination of properties that include translucency, neutral alkoxy cure, and shelf stability in conjunction with primerless adhesion to polyacrylate.